A typical liquid crystal display (LCD) is capable of displaying a clear and sharp image through thousands or even millions of pixels that make up the complete image. The liquid crystal display has thus been applied to various electronic equipment in which messages or pictures need to be displayed, such as mobile phones and notebook computers. A liquid crystal display generally includes a liquid crystal panel for displaying images.
In a TFT-LCD (thin film transistor liquid crystal display) device, spacers are provided between two substrates of the TFT-LCD device to maintain a cell gap between the substrates. The spacers may be plastic beads, glass beads, or fiberglass beads. During manufacturing of the TFT-LCD device, in general, the spacers are first distributed onto one of the substrates. The method of distribution may, for example, be a spraying method. Once the TFT-LCD device has been assembled, the spacers keep the cell gap consistent, in order that the TFT-LCD device can work accurately and reliably. However, many or most of the spacers are located in a display region of the TFT-LCD device. These spacers may cause light scattering, which is liable to generate white point defects. Thus, the contrast and the display performance of the TFT-LCD device are impaired. For this reason, photo spacers formed by a photolithographic process have been developed to replace conventional plastic beads, glass beads, or fiberglass beads. Various dimensions and positions of the photo spacers can be provided in order to avoid affecting the transmission of light, while at the same time ensuring a uniform cell gap. Thus, the display performance of the TFT-LCD device is enhanced.
Referring to FIG. 5, a typical liquid crystal panel 2 includes a first substrate 21, a second substrate 22 parallel to the first substrate 21, and a liquid crystal layer 23 sandwiched between the first substrate 21 and the second substrate 22.
The first substrate 21 includes a plurality of parallel scanning lines (not shown), a plurality of parallel data lines (not shown) perpendicular to the scanning lines, a plurality of thin film transistors (TFTs) 29 provided in the vicinity of points of intersection of the scanning lines and the data lines, and a first alignment film 201. Each of the TFTs 29 includes a gate electrode 291, a source electrode 292, and a drain electrode 293.
The second substrate 22 includes a light-shield film 26 configured for shielding light rays, a plurality of color filters 25, a common electrode layer 24, a plurality of first photo spacers 27, a plurality of second photo spacers 28, and a second alignment film 202.
Referring also to FIG. 6, the light-shield film 26 is disposed at an inner surface of a base substrate (not labeled) of the second substrate 22. The light-shield film 26 is generally formed like a grid, thereby defining a plurality of display regions arranged in a regular array. The color filters 25 are formed at the display regions respectively. The common electrode layer 24 is formed on the light-shield film 26 and the color filters 25. The first photo spacers 27 and the second photo spacers 28 are disposed on the common electrode layer 24. Each of the first photo spacers 27 corresponds to one of the drain electrodes 293 of the first substrate 21. Each of the second photo spacers 28 corresponds to one of the source electrodes 292 of the first substrate 21. The second alignment film 202 is formed on the common electrode layer 24, the first photo spacers 27, and the second photo spacers 28. An alignment direction of the second alignment film 202 is perpendicular to an alignment direction of the first alignment film 201. The gate lines, the data lines, and the TFTs 29 of the first substrate 21 are located corresponding to the light-shield film 26.
The common electrode layer 24 is a transparent layer made from indium tin oxide (ITO) or indium zinc oxide (IZO). The first and second photo spacers 27, 28 are made from macromolecular material, and have different heights. In particular, a height of the second photo spacers 28 is slightly greater than a height of the first photo spacers 27. The heights of the first and second photo spacers 27, 28 can be reduced when the first and second photo spacers 27, 28 are forcibly compressed. The second photo spacers 28 are configured for maintaining a cell gap between the first substrate 21 and the second substrate 22. The first photo spacers 27 are configured for supporting the cell gap in case the second photo spacers 28 are pressed excessively.
During the fabrication of the first alignment film 201 and the second alignment film 202, a rubbing process is generally adopted. A brush is generally used to brush along the predetermined alignment directions of the first alignment film 201 and the second alignment film 202. However, because the first photo spacers 27 and the second photo spacers 28 have certain heights and are all arranged on the second substrate 28, alignment defects may occur when the second alignment film 202 is rubbed in areas adjacent to the first photo spacers 27 and the second photo spacers 28.
Referring to FIG. 7, an enlarged view of part of the second substrate 22 is shown. The alignment direction of the second substrate 22 is along the direction of the arrow “R”. When the first and second alignment films 201, 202 are brushed during an alignment process, some small areas of the first and second alignment films 201, 202 adjacent to the first and second photo spacers 27, 28 are blocked from brushing by the first and second photo spacers 27, 28. Thus, small areas adjacent to the first photo spacers 27 along the direction R (shown in dashed lines) are alignment defect areas, and small areas adjacent to the second photo spacers 28 along the direction R are also alignment defect areas. The alignment defect areas and the display regions (i.e. the color filters 25) define overlapping areas 203. At these overlapping areas 203, liquid crystal molecules of the liquid crystal layer 23 are liable to be misaligned. Accordingly, the image quality of the display regions is reduced. Therefore, a liquid crystal display utilizing the liquid crystal panel 2 has impaired performance.
What is needed, therefore, is a liquid crystal panel that can overcome the above-described deficiencies.